Paper guide rollers are used in order to guide paper in predetermined paths. Freshly printed paper webs frequently must be guided in such a way that the freshly printed surface contacts a guide roller. It is difficult to prevent smearing of the freshly printed subject matter as it passes about the guide roller. Typically, such guide rollers are not independently driven but, rather, are carried along by frictional engagement with a paper web passing thereover.
The German Utility Model G 73 45 259 describes a system in which a cylindrical base body, forming a paper guide roller, has a coating thereon, applied by a flame spray process. The coating is a single layer of adjacently positioned droplets projecting from the carrier material. Tiny, essentially funnel-shaped depressions remain between the projecting droplets. These projections, with the funnel-shaped depressions therebetween, furnish a rough surface, so that slip between the frictionally driven roller and the paper web which runs over the roller is effectively avoided. The friction is sufficient to carry along the paper guide roller.
The droplets contain a high percentage of chromium. Thus, the effect is ink repellent. The paper guide roller, however, has a rather coarse, rough surface, and the projecting droplets have sharp edges. Thus, folds or creases in the web rolling off around the roller cannot be compensated. The coarse roughness of the surface of this roller additionally causes difficulties in cleaning.
It has been proposed to use a rubber-like carrier layer and embed glass balls therein, to form a surface cover layer for a guide roller. Such coatings have been referred to as sphere coatings. The glass balls or glass beads form a hard surface which, further, is ink repellent, or oleophobic. Such micro-coated layers can be used only with driven rollers, however, since the surface is too smooth, and does not permit drive of the roller merely by friction with the engaging web. The packing density of the glass balls must be sufficient so that no ink will deposit on the surface of the roller between the glass balls, since the rubber layer has oleophilic characteristics.